Here are some of the changes to Buildroot [master] in his [jumpnow] branch that all worked for me.
- Newer versions of the Linux kernel and RPi firmware
- Some custom applications primarily as an experiment in how to add custom packages to Buildroot. The source for all of them are public github repos.
- serialecho - a C, Makefile based app
- tspress - a Qt5 Widgets GUI app using qmake
- pytouch.py - a PyQt5 app
- Custom Buildroot defconfigs to support my images for the RPi boards.- Sample rootfs overlays to customize conf files. <- This is the important one!

Some patches to the kernel build so that the RPi DTS overlays (DTBOs) are built from the kernel source and not just downloaded from the RPi firmware github repo. This make its a little easier (at least for my workflow) to include custom dts overlays when you need them by just including them as kernel patches.

I managed to build a functional image...boots to a command prompt and does some commands...but now I am all dressed up with no place to go...how to find/install applications? I recommend using copy/paste on the commands...memory or finger failures lead to build errors.

For anyone contemplating this, the buildroot process will use about 2.5 Gig if you are on a metered connection (as I am). The saving in boot time may not be worth the build time plus the acquisition of applications.